Added (some) documentation
...albeit far from being complete, as always.
## Building VDB from Sources
### Building GNU Debugger for use with VDB
See [GDB building instructions][3] from [jv:libgdbs][4]
### Building VDB
*Visual / VM Debugger* is a part of [Smalltalk/X jv-branch][1] since version
8.0.0. To build VDB, just follow instructions how to [build Smalltalk/X jv-branch][2]
[1]: https://swing.fit.cvut.cz/projects/stx-jv
[2]: https://swing.fit.cvut.cz/projects/stx-jv/wiki/Documentation/BuildingStXWithRakefiles
[3]: https://bitbucket.org/janvrany/jv-libgdbs/src/tip/doc/GDB.md
[4]: https://bitbucket.org/janvrany/jv-libgdbs